I've recently started using a slow cooker and I was thinking about recipes that could be cooked for days. My main concern is if there are any side effects for leaving food cooking for days that would make this plan unfeasible (dangerous to try). Since it is at cooking temperature, there wouldn't be any reason to worry about bacteria growing on the food. Liquid would be lost over time, which could result in burning if left unchecked, but if I add more every morning/night as needed, that too wouldn't be a problem. All I can see is that most recipes wouldn't end up tasting as well, but undesirable isn't equal to dangerous.

There just seems to be something absurd with the notion of leaving food cooking for 5 days or even 2 weeks without there being any dangers, but I'm having a hard time figuring out what they would be.

You've answered the food safety question yourself. So why would you want to leave anything cooking in a slow cooker for five days or two weeks? It is kind of absurd.
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Carey GregoryOct 1 '13 at 3:46

3

Who would want to eat a century egg or fish that hasn't been thoroughly cooked? What about fried tongue or 'milk' from almonds/soy? What you or I call absurd another may call dinner. Beans that turn to mush? Perhaps that is a new food or part of a new dish? Perhaps something too woody to eat right if cooked regularly will soften and become edible when cooked this long? I'm not saying it will end up with something worth eating, I was just wondering if it could safely be eaten.
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LawtonfogleOct 1 '13 at 13:05

@Lawtonfogle Century eggs aren't made like this. Eggs or fish cooked for hours (let alone days) will be overcooked. If you're going to cook something this long there's not much point frying it, and if you're just trying to soften it up before frying, it doesn't take days. And if you want mush, you can generally get it with a few hours of cooking (at most half a day) and a little mashing. I'm not saying it's useless, but the real uses for cooking this long are fairly limited.
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Jefromi♦Oct 2 '13 at 1:07

A note of warning about newer slow cookers with digital controls -- some of them will automatically shut off after a period of time (less than a day). If you're thinking of doing this, you want to use a slow cooker with a manual switch so you don't run the risk of it shutting off on you.
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JoeJun 9 at 9:16

7 Answers
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It's safe. All that matters for safety is that the food stays out of the danger zone (above 140F).

But it sounds like a pretty reliable way to overcook things. Perhaps that's why it sounds absurd to you? Slow cookers tend to be somewhere between simmer and light boil (probably at least 180F), and there's very little that won't be fully cooked after half a day at those temperatures. If you cook for days, you'll start turning beans and vegetables to mush, and may manage to make meat tough from overcooking. So at best it's pointless, and at worst it's going to mess up your food.

Additionally, the longer the food is boiled, the more of its aromatic flavor compounds will be lost due to evaporation leaving. Even overcooking just a few hours at a simmer can lead to muddy, dull flavors...
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DidgeridrewFeb 25 '14 at 19:41

I often cook pork shoulder steaks at 60°C (140°F) for 48 hours sous-vide and as your shoulder is an intact piece of meat you really only need to be worried about any bacteria on the surface of the meat; presuming the shoulder is submerged in liquid, a cooking time of 24 hours at 60°C is long enough to pasteurise the surface and the interior. There's a good thread on eGullet that, while about sous-vide, is applicable here.

Also, in the massively unlikely scenario that the pork is infected with Trichinosis the USDA guides state that holding the meat at 140°F for 1 minute will kill the parasite

The main purpose though of cooking your shoulder I presume is to tenderise it and at temperatures of 140°F you won't get the characteristic falling apart texture associated with braised meat.

What you're suggesting was effectively a form of food preservation in medieval times -- just keep the food warm at all times.

This works best if you keep adding something to it (not just liquid), so there's something that hasn't completely turned to mush ... and you might want to hit it with a shot of vinegar or citrus to perk it back up when serving. You can also add acid while cooking to slow down the breakdown of potatoes and onions (and maybe other vegetables), but in the long-cooking you'll lose some of the brighter notes.

If you try it with stew, you're going to end up with something closer to ragù by the time you're done. Personally, I like that in a pot roast, but I know some people aren't fans.

You could also add some fresh, mostly uncooked items when serving, that just need to be warmed through. (eg, fresh or frozen peas (not canned), been sprouts, or some diced bell pepper or onion, as appropriate for the dish).

The technical answer is, as long as the food stays above 140 F / 60 C, pathogens are not going to grow. This is the hot equivalent to refrigeration. Note that there are probably no studies of holding foods at these temperatures for truly extended periods, but you pays your money and you takes your chances.

On the other hand, even with the lid on, over time, water is going to escape, and the food will begin to dry out. Even slow cooking meats like pork shoulder or ox tails can and will become overcooked and tough over time, even if there were no moisture loss.

With the fringe exception of a stock pot that is continually replenished, I cannot think of a single good reason to do this.

Even with refrigeration, a lot of food spoils after a few days. Could the same happen if you are keeping it hot?
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LawtonfogleSep 30 '13 at 17:56

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That is the part where I doubt studies have been done, but since the idea is so absurd already for reasons both Jefromi and I have enumerated, I am not going to go looking for any such science.
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SAJ14SAJSep 30 '13 at 17:58

The USDA recently lowered the recommended safe cooking temperature of pork to 145°F (60°C), from the long-time standard of 160°F (70°C). However, this really applies more to lean cuts like loin - for a bigger cut like your shoulder, 165-180°F (75-80°C) is probably a safer bet.

Cooking at that temperature for 24 hours should give you no problems; do test it with a probe thermometer to make sure it is the right temperature all the way through.

190°F (90°C) would have been slight overkill even before the change, and 275°F (135°C) is just crazy.

Can you explain why you think the fat content has an effect on safe cooking temperature?
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Josh CaswellOct 5 '12 at 16:24

Lean meat and fat conduct heat differently. That is, if you put similar pieces of lean meat and fat in the same water bath, the time it takes the heat to reach the center will differ. The connection to safety? The combination of time and temperature determines how many bacteria survive.
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soegaardOct 5 '12 at 18:19

@ElendilTheTall using º for degree symbol looks weird, or very weird in some fonts, try ° which can be generated with &deg;
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TFDOct 5 '12 at 20:33

They both look the same to me. <shrug>
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ElendilTheTallOct 6 '12 at 7:38

Perpetual soup, which is exactly what you're talking about here, was a staple in many old world diets. It's still done in many places around the world today. Poland, Alaska, Russia, and many of the colder environments where it's harder to get food in the winter times. There is a risk to all things cooking no matter the preparation you take.

Perpetual soup is actually less meat and vegetables and more the scrap of what you've already cooked. The bones and perhaps edible organs. If doing this in a crock pot it would be best to simply let it cook, adding water as needed.

I do this myself, my crock has been going for almost a month now. Mind you I empty it into a roasting pan clean it and then add my mix back once per week. All things considered, I've never had any problems with flavor and the broth is amazingly nutritious.

The only real issue I've seen, from my own mistakes, when I tried this a couple years ago was adding directly on top of what is already in the pot. Anything you add needs to be under what you've already cooked and only when you're done pulling from it for at least four hours. It takes time but eventually you can get down a schedule for adding to it that works for you.

Pork needs to be cooked throughout. It needs to be above 72°c for most bacteria to die. As long as you have increased the heat and let it alow cook above that head for a bit you will be fine. Remember that these heats are just guide lines but if you are serving it to other people then it is probably best to adhere to them.